The present invention relates to monitoring the properties of a surface, specifically, monitoring the surface using electromagnetic radiation. In the most generic sense, surface means the interface between any two media. It can be between gas and a solid, gas and a liquid, between two liquids, between a liquid and a solid, or between two solids, etc.
At an interface between two media one would like to be able, at different times and/or for different applications, to see what the chemical, mechanical, and molecular properties of that interface are. A nonintrusive, nondestructive methods to investigate the interface is desirable. Further, the method should not impose restrictions based on the particular environment around that interface. Because of this, one often uses an electromagnetic radiation technique. Thus, visible light, ultraviolet light, infrared, x-rays, radio frequencies or any other electromagnetic radiation may be used. The frequency at which one or the other interface media is transparent will determine what type (e.g., visible, ultraviolet, etc.) of signal is chosen so that a surface specific response is obtained. For example, linear reflection optical techniques (i.e., the output frequency equals the input frequency), do not provide what is called a surface specific response. Rather, interference from either one or the other media through which the signal must travel or be reflected will result.